This study contributes to the literature examining the effect of Medicaid coverage on physical health and health care utilization. We exploit variation in Medicaid eligibility and coverage provided by the 2009 Children's Health Insurance Program Reauthorization Act (CHIPRA), which expanded Medicaid coverage to legal permanent resident pregnant women (LPRPW) within their first five years living in the United States. Fourteen of 41 states not previously using state-only funds to provide health insurance to LPRPW enacted CHIPRA. We use this policy variation as a natural experiment, studying the effects of CHIPRA within adopting states compared to non-adopting states. We remove from our analysis 9 states using state-only funds to provide Medicaid coverage to LPRPW. We match this policy variation from CHIPRA onto all birth records in the United States from the period of 2003 to 2012. We exploit fortunate timing in payment source information being added to the birth record data in 2009, shortly before CHIPRA implementation in select states. Our first model is a reduced form model to explore the effect of CHIPRA implementation on outcomes of payment source (i.e. private insurance, Medicaid, or no insurance), prenatal care visits, premature births, low birth weight births, abnormal birth conditions, and infant mortality. We propose a difference- in-differences analysis, comparing outcomes between LPRPW residing in states that implemented CHIPRA relative to LPRPW in comparison states. Our results provide an estimate of the extent of crowd-out of private insurance when Medicaid is expanded, as well as an estimate of how CHIPRA influenced prenatal care visits and birth outcomes, including for LPRPW with a higher probability of being uninsured prior to CHIPRA implementation. Our second model is an instrumental variable model to study the impact that having Medicaid has on prenatal care utilization and birth outcomes, exploiting variation in Medicaid eligibility from CHIPRA. The proposed research will provide additional information to states deciding whether to expand their Medicaid programs through the ACA and/or CHIPRA. The proposed project will also lay a foundation for the applicant to continue studying how Medicaid expansions influence health care utilization and health outcomes.